SD is 12. It's a surly age. She's still learning politeness. To me, the 'good morning' is the equivalent of teaching them please and thank you. Model it. Say it first and she should echo it. After a while, maybe a long while, she'll start saying it first. Get DH involved only if she is not echoing your greeting.

Was for DH to teach her to say "Goog morning ". It's the parents fault for not teaching her to be a person 

SD13 comes and goes without saying a word. Literally walks out the front door while myself and DS3 are standing there. Maybe it's passive agressive to some, but I say outloud to DS3 "Say/wave bye to _______!"  Even if SD13 pretends like we don't exist, I at least want to teach my own child how to be polite even if the other person isn't. 

Basic bare minimum. Expectation of treating someone in the household with the most basic of politeness is a REQUIREMENT in my book.

When there was a conflict a while ago, I heard that Powersulk was saying that if I dont get a hello from her I get upset. Well, sure, surly. Ive also talked with her in conversation.

Shunning is a form of abuse.

Oh, the SDs used to ignore me too when I was picking up/dropping off. After a while of me saying hello/goodbye (this started of course around ages 12), I just ignored them too.  

They did this to DH too and he was NOT happy about it, but nothing changed. 

YSD17 is better now and always says hello or goodbye.

 With teens nowadays the bar is set so low unfortunately especially with step kids who bio parents have deemed that basic expectations for respecting people who provide for them is making them "suffer"

No most kids have minimal to no home training. So I would not expect a 12 year old to initiate a hello but I WOULD expect them to reply after I greet them whilst constantly reminding them to "greet their elders (especially the ones who provide for them)" and praise them for doing what they're supposed to do. 

This is the parents fault. To let this go on.  Not the SP. but the bio parents. To say every morning .. Good morning. Say good morning or lose your cell phone.  We will see how fast this solves the problem.  Not if you don't say good morning I will have the talk with you [again] 

'Kids are a lump of clay that needs to be molded.  From the beginning..  Kids who are disrespectful,, comes from there parents allowing this to happen. Not molding them in the right way.  I am old fashioned.. I believe the parents are in charge. And things go the parents way. Not a 12 yo controlling the household 

Oooh definitely SD should be saying good morning. My 3 year old says it first to them and DH and I! SS and SD walk out to the kitchen and DD3 says 'good morning! How was your sleep?'. This is basic good manners and etiquette. It is not hard to teach children this. It's lazy parenting if children don't do this.

SD sometimes doesn't acknowledge my existence when she emerges into the kitchen and gives DH a hug and a morning greeting. He immediately tells her to say good morning to me and not be rude. SS even if he is tired will always give me a hug good morning. SD if she does hug me only does it as she feels she has too. I'm not fussed about the hug I just want acknowledgment I exist in my own home. It's respect. Your DH should definitely tell her to say it first to you. I always said good morning to my parents when I was a child. It's just how I was brought up. 

My partner and I have been living together for nearly 4 years and she never greets me either nor says a single word to me if I don't talk to her first. It can be very frustrating especially if your DH doesn't support you.

Have you asked your DH to talk to her about it? (in a nice way)

So, don't let her in the car until she verbalizes a polite greeting. Lather.... rinse... repeat.

Don't let her ignore you.  Walk up to her and give her a clear "Good morning". Or "Hello". If she walks into the room and does not greet you, give her a pointed "We say hello/good morning in this family. Good morning!"

Model the behavior you are demanding and .... demand.

Every time.

SS10 often blank stares at me or others when we come in contact. We have been over it 1000x of greeting people, he lives with us & his father says it's the weirdest thing he has ever seen. Same with manners, he doesn't always remember please and thank you even though it is reminded EVERY NIGHT at dinner like it was the first time. I can't stand it, it infuriates me. It puzzles SO & he thinks SS has loose wires. Most of the time I just want to slap & shake the wires & hope they start working!

My SS who is almost 20, rarely said hi or bye to me in the morning at breakfast or as he left for school growing up and he lived with us full-time or more than half-time. He also completely ignored my now 8 year old EVERY single day. And, I would greet him, yet get ignored whether purposely or through complete inattention.

I forced my husband to make some hard decisions after SS graduated from high school, basically saying that SS had to find his way as an adult out of our house, whether it be at college (though he was not a good student) or with roommates and a job OR DH would face losing his wife and little kids. SS left, moved in with his mom, and after losing about 4 jobs, he got it together and has kept a good job for 9 months. 

Now, he visits us weekly. He no longer ignores DS or DD and actually plays with them. He is more than tolerable on his visits. I think what happened is that he matured a bit, but also the little kids have no ill feelings towards him. They don't know/remember what he was like. They only know that he is their brother. They have always just been Uber excited to see him and I don't think he could've continued to ignore them and consider himself a likeable person. He even talked about getting them a Christmas gift. I really never thought he would ever have any interest in them unless it had to do with himself (which still could be the case, but at least it doesn't seem like it anymore)

So, maybe there is hope that things will change.